Susceptibility of phytopathogenic bacteria to wheat purothionins in vitro

Purothionins are basic polypeptides with antimicrobial properties that are present in the endosperm of wheat and other cereal species. Susceptibility to wheat purothionins among phytopathogenic bacteria of the genera Pseudomonas, Xanthomonas, Agrobacterium, Erwinia, and Corynebacterium has been investigated. Sensitive strains have been found in all of these genera except Agrobacterium (the only strain of A. tumefaciens available proved to be resistant). Minimal inhibitory concentrations (MIC) with partially purified crude purothionins ranged from 1 mug/ml for C. sepedonicum (C.5) to 540 mug/ml for E. amylovora (E.3). Minimal bactericidal concentrations (MBC) were not higher than twice the MIC value, except for C. poinsettiae (C.4) (MBC/MIC = 8). Purothionins alpha and beta, obtained by carboxymethyl-cellulose column chromatography, were tested against P. solanacearum (P.2) and X. phaseoli (X.2); alpha purothionin was more active than beta against X.2, and beta more active than alpha against P.2. This suggests a relationship between polypeptide sequence and specificity of action.